The shortest good Halloween poem I’ve found is John Ciardi’s limerick, “The Halloween House,” an amusing send-up of children’s tendency to pretend they’re not afraid of haunted houses. It begins: I’m told there’s a Green Thing in there.
And the sign on the gate says BEWARE!
For copyright reasons, I can’t quote all five lines of the poem. But you can find “The Halloween House” in Ciardi’s The Hopeful Trout and Other Limericks (Houghton Mifflin, 1992), illustrated by Susan Meddaugh, which is out of print but on the shelves of many libraries. You can also find “The Halloween House” in Scared Silly! A Halloween Book for the Brave: An Arthur Adventure (Little, Brown, 64 pp., $7.95, paperback), illustrated by Marc Brown, which is in print and available through online and other booksellers. The Hopeful Trout is used in grades 2 and up in schools. Scared Silly! has gentle not-so-scary poems, jokes and more for preschoolers, written by a variety of authors.

Thanks for the comment on Dante. Sometimes when I decide to read a classic written in a foreign language, I spend weeks thinking about which translation to read. So it’s helpful to have comments like yours (especially given that Sayers is better known to many than Ciardi, so they might reach for her first).